Automatic gas well flow control

ABSTRACT

An automatic gas well control device is disclosed which optimizes gas well production by allowing the well to produce only while adequate flow rates are maintained. The device includes a control valve in the discharge line which is responsive to the pressure differential between the tubing and sales lines and to the rate of discharge from the well as measured by differential pilot valves. One pilot valve sends a pneumatic signal to close the control valve when the rate of production drops below a predetermined level to shut-in the well to permit gas pressure to build to a level for acceptable production. Another pilot valve monitors sales and tubing line pressure and operates to send a signal to the control valve to open the control valve only when the tubing pressure exceeds the sales line pressure by a predetermined differential.

United States Patent 11 Watson, Jr.

[ 1 AUTOMATIC GAS WELL FLOW CONTROL [75] Inventor: David Reed Watson, Jr., Midland,

Tex.

[73] Assignee: Compatible Controls Systems, Inc.,

Midland, Tex.

[22] Filed: I Apr. 17, 1973 [21] Appl. No.: 352,043

[111 3,863,714 [451 Feb. 4, 1975 Primary Examiner-David H. Brown Attorney, Agent, or Firm-Richards, Harris & Medlock [57] ABSTRACT An automatic gas well control device is disclosed which optimizes gas well production by allowing the well to produce only while adequate flow rates are maintained. The device includes a control valve in the discharge line which is responsive to the pressure differential between the tubing and sales lines and to the rate of discharge from the well as measured by differential pilot valves. One pilot valve sends a pneumatic signal to close the control valve when the rate of production drops below 'a predetermined level to shut-in the well to permit gas pressure to build to a level for acceptable production. Another pilot valve monitors sales and tubing line pressure and operates to send a signal to the control valve to open the control valve only when the tubing pressure exceeds the sales line pressure by a predetermined differential.

13 Claims, 5 Drawing Figures AUTOMATIC GAS WELL FLOW CONTROL The present invention relates to an automatic flow control for gas wells and more particularly relates to a regulating device which is responsive to fluid pressure and fluid flow to intermittently operate a motor control valve to shut-in the well to allow the well pressure to build a sufficient level to expel gasfrom the well.

Oil production economic requirements demand that production of gas wells be optimized. In order to maintain production from a low volume producing gas well, regulation of the gas well is required. It is recognized that it is necessary to occasionally check the flow of fluid from a well in order to allow internal pressure within the well to build to a sufficient level to deliver the desired rate of flow from the well. It is also well known that flowing gaswells are adversely affected by accumulations of liquid within the well casing or tubing which may cause discharge from the well to fail due to static pressure build-up in the tubing or casing. It is therefore common to provide automatic controls associated with gas wells which operate on a timed cycle to periodically vent the well to effect forcible expulsion of the accumulated liquid from the tubing string in the well bore. After the well has been vented or blown down, the control valve is closed and the well allowed to resume its normal production.

While such intermitting or periodic venting of gas wells is common, this procedure has several important disadvantages. In these venting operations, automatic intermitting of the well occurs regularly ata predetermined and preset timed intervals regardless of whether an excessive amount of liquid has actually accumulated in the well string. When only a small quantity of liquid has accumulated, automatic venting of the well is unnecessary and interferes with production. Unnecessary venting also results in the expulsion and considerable loss of gas from the well. Further, in many areas, open venting of gas wells contravenes the regulations of governmental agencies which regulate the petroleum industry and can subject the operator to various sanctions and penalties.

In order to avoidthe disadvantages of conventional intermitting apparatus and to reduce wasting and loss of natural gas inflowing wells, several other types of automatic we'll controls can be found in the prior art. For instance, it is common to use various gas injection or gas lift systems for improving production from gas wells by raising the pressure in the well. The introduction of a gas medium, such as compressed air, may be controlled in response to the pressure existing within the well casing or tubing or may be controlled in response to the level of the liquid within the well bore. A rise of liquid in the well results in a loss of pressure and can be used to control the injection of gas.

A more recent approach to increasing well production and preventing unnecessary venting of gas wells is found in U.S. Pat. No. 3,266,574. This patent shows a control device in which a liquid discharge line communicates with the tubing string in the well across a motor valve assembly. A cyclic control device is associated with the control valve and is responsive to the pressure differential between the casing and the tubing to operate the valve. Upon accumulation of liquid in the tubing, an attendant pressure decrease occurs in the gas pressure in the tubing string. When this pressure reaches a predetermined level with respect to the casing pressure, the control valve is opened to eject the liquid accumulation from the well string to the atmosphere in order to reduce interference of the liquid with the gas flow from the well.

The present invention provides a differential gas well control which automatically and periodically upon preselected conditions, shuts in the well for a period of time until the pressure within the tubing builds to a predetermined level. The control includes a motor valve in the discharge line operated by pressure pilot valves responsive to the rate of flow and the differential existing between the sales and tubing line. When a predetermined differential pressure between the sales and tubing line is reached, the gas flow from the well is resumed and is allowed to continue until the rate of flow drops below a certain level. When the flow rate drops, the well is shut-in and the control cycle starts all over again. Once the control of the present invention is set at the proper flow rates, it will continue to operate automatically shutting in the well and resuming flow in response to the predetermined well conditions.

The advantages of the control of the present invention are numerous. By monitoring the tubing and sales pressure and the rate of flow, the well is shut-in prior to excessive fluid accumulation in the tubing. Shuttingin of the well allows the pressure within the tubing to recover to an acceptable level for adequate operation of flowing gas from the well. The necessity of blowing down or venting the well is eliminated and wasteful or possibly illegal venting is avoided. Further, with the control of the present invention low volume producing gas wells, as for example, those wells producing below 5 million cubic feet of gas per month may be economically operated. Generally, gas wells having this limited production are required to be plugged as not being economical. With the control of the present system, such wells can be maintained in production.

The above and other objects and other advantages of the present invention will become subsequently apparent from a reading of the accompanying specifications, claims and drawings in which:

FIG. 1 is a diagrammatic view showing a typical gas well equipped with the automatic cycle control mechanism according to the present invention;

FIG. 2 is a detailed view of the control system of the present invention;

FIG. 3 is a schematic representation of the controller of the invention;

FIG. 4 is a schematic representation showing the alternative embodiment of pilot valve 42 as operated by an electrical operator and micro-switch;

FIG. 5 is a schematic representation showing the alternative embodiment of the control valve 22 as a solenoid operator.

Referring now to FIG. 1, the numeral 10 generally designates a gas well having a casing 11 extending into subterranean gas bearing formation 12. Casing ll terminates at an open or perforated bottom 14 to permit gas from formation 12 to be admitted to the interior of casing 11. The upper end of casing 11 terminates at conventional well head 18. The tubing string 16 extends through well head 18 and into casing 11 terminatng at a location above the lower end 14 of the casing. An annular space 19 is located between the interior of casing 11 and exterior of tubing string 16. The upper end of tubing 16 is provided with a discharge line 20 which communicates with sales line 24 across motor control valve 22.

The well shown inFlG. l is typical, it being understood that casing 18 may terminate at a packing above the formation 12 and below the surface. Also, the well may be operated with a single string or pipe for extraction of gas excluding annular space 19.

As is well known, gas and liquid enter the casing at bottom end 14 and at perforations in the casing wall. The pressure of the well bore, that is, the pressure existing at 14, causes the gas from formation 12 to enter the well and rise through tubing string 16 and be discharged into a delivery point such as sales line 24. As long as the lower end of tubing string 16 is not submerged in an accumulation of water or oil in the lower part of the well casing, the pressure within tubing 16 and the annulus 19 surrounding the tubing will be substantially equal. However, as water, oil and other liquids infiltrate into the lower part of the casing, the lower end of tubing string 16 will become submerged. When this occurs, the pressure existing in the annulus 19 will cause the liquid to rise within tubing string 16, resulting in a decrease in gas pressure within the tubing string 16. As the pressure within tubing 16 decreases the flow of gas from the well is substantially reduced.

As pointed out above, conventional control systems rely on the venting of the fluid within tubing string 16 to again establish pressure conditions within the well which will afford an acceptable rate of flow from the well, However, with the present invention, in order to compensate for these problems, the well is allowed to produce when the pressure differential between the tubing and the sales line is sufficient to unload fluid at a satisfactory rate. The well will remain open until the velocity or rate of flow from the well decreases to a point that the fluid begins to fall back and accumulate in the tubing. At that point, the well flow is terminated or shut-in and the shut-in condition is maintained until the pressure differential between the tubing line and sales line reaches a predetermined level.

Again, referring to FIG. 1, the controller of the present invention is'generally indicated by the numeral 25, and is operatively connected by line 32 to diaphragm controller 30 of motor control valve 22. Motor control valve 22 is normally biassed to a closed position by a spring, not shown. As will be explained in greater detail hereafter, controller 25 automatically responds to monitored pressure and flow conditions and periodically pressurizes or depressurizes the diaphragm chamber of controller 30 thereby causing valve 22 to accordingly open or close.

Controller 25 regulates the discharge flow rate through line 20 by monitoring the differential pressure across orifice 35 at signal lines 36 and 38. Controller 25 also monitors the differential pressure existing between the tubing and sales line at lines 36 and 40. Controller 25 functions to send a signal to diaphragm controller 30 to open motor control valve 22 when a predetermined differential exists between the pressure in the sales and tubing lines as applied to pilot valve 42 by signal lines 36 and 40. Controller 25 will shut-in the well or terminate flow from the well when the flow rate through line 20, as measured by the differential pressure in signal line 36 and 38, and applied to pilot valve 44, falls below a preset rate.

The controller for the present invention is shown in greater detail in FIG. 2. Referring to that figure, the controller 25 includes pilot valves 42 and 44 which are similar in construction. Pilot valve 42 includes an outer housing 46 defining a pressure chamber 47 at the lower part of the housing. Pressure chamber 47 is divided into upper and lower diaphragm chambers 48 and 52 by transversely extending diaphragm 50. Upper diaphragm chamber 48 communicates with the pressure in the sales line via signal line 40. Lower diaphragm chamber 52 is connected at inlet 54 to signal line 36. Spring 56in diaphragm chamber 48 exerts a downward biassing force against diaphragm 50. The pressure in lower diaphgram chamber 52 must overcome the combined pressure force exerted against the surface of the diaphragm in chamber 48 and the force of the spring 56. Plunger 58 axially extends in housing 46. The lower end of plunger 58 is located immediately adjacent the upper surface of diaphragm 50. Preferably, diaphragm 50 will include a small bearing surface at the point of contact of plunger 58 to prevent wear or rupture of the diaphragm. It will be seen that when the pressure in diaphragm chamber 52 is sufficient to overcome the combined biassing force exerted in chamber 48 and spring 56, diaphragm 50 will urge plunger 58 upwardly.

Three-way pneumatic valve 60 is mounted in the upper end of housing 46. Valve 60 is a normally closed pneumatic valve of the type designated Model MJV-3, manufactured by the Clippard Valve Company, cincinnati, Ohio. Actuating plunger 62 controls the operation of valve 60 and is aligned with plunger 58. When plunger 62 is depressed, supply pressure admitted to valve 60 at inlet 63 is internally communicated with valve outlet 64.

To provide adjustment of the response and sensitivity of the device, valve 60 is carried on bracket 68 and secured to cover plate 66 of valve 42 by spring loaded adjustment screw 67. Screw 67 is in threaded engagement with bracket member 68 and can be turned to raise or lower the position of valve 60. Accordingly, this will cause adjustment of associated plunger 62 with respect to plunger 58, moving actuating plunger 58 closer or away from plunger 62.

The construction of pilot valve 44 is essentially the same as the construction of pilot valve 42 as described above. Accordingly, the same reference numerals will be used to identify similar elements, distinguished by an appended letter a. Pilot valve 44 has a housing 46a which defines lower pressure chamber 47a subdivided by diaphragm 50a into upper diaphragm chamber 48a and lower diaphragm chamber 52a. Axial plunger 58a is aligned to engage plunger 62a of three-way pneumatic valve 60a. Valve 60a is adjustably secured by screw 67a and bracket 68a to cover plate 660 of pilot valve 44. Lower diaphragm chamber 52a is connected at fitting 54a to pressure line 36. Upper diaphragm chamber 480 is in communication with the pressure from the downstream side of orifice 35 via line 38. Three-way valve 68a communicates with the source of regulated air pressure at inlet 63a and discharges a signal pressure at outlet 64a.

The pneumatic gas supply for the system is provided by conventional pneumatic regulator 70. Regulator 70 is connected to a source of air pressure 73 across filter 74 and line 76. The term gas is used broadly to mean any appropriate pneumatic supply, for example, air; gas from the well, butane, or similar sources may be utilized. Regulator 70 maintains a substantially constant supply pressure discharging at outlet 78 and tee 80. Tee 80 connects to inlet 63 of valve 60 by supply line 81 and to inlet 63a of valve 6011 by supply line 82. Outlet 78 supplies a regulated air supply to three-way valve 86 by line 87.

Valve 86 is a standard three-way pneumatic valve such as the Model MJV-4D, manufactured by the Clippard Valve Company of Cincinnati, Ohio. The outlet 91 of valve 86 communicates with cross 88 across oneway check valve 117. One outlet of 88 is connected by line 32 to the controller 30 of valve 22.

Valve 86 has a body 90 defining an internal bore which houses a'reciprocal valve spool having plungers 94 and 96 which oppositely extend from the valve spool. When plunger 94 is depressed, reciprocating the valve spool of valve 86 tothe right as seen in FIG. 2, inlet 85'is placed in communication with outlet 91 supplying a pressure signal across valve 86 to control valve 22. Conversely, when plunger 96 is depressed, the valve spool is moved leftwardly to bleed off the regulated supply pressure and discontinue communication across valve 86.

Small pneumatic cylinders 98 and 100 are secured on opposite sides of body 90 of valve 86. Cylinders 98 and 100 each house a reciprocating piston member 99 and 101, respectively. Pistons 99 and 101 are aligned to contact and reciprocate plungers 94 and 96 when cylinder chambers 103 and 105 respectively are pressurized. Cylinder chamber 103 is connected to valve 60 by line 106. Pressure chamber 105 of valve cylinder 100 is connected to valve 60a by line 108. Tee 110 and line 112 communicates the outlet 64a of valve 600 with volume chamber 114. One-way check valve 116 is provided in line 112 to prevent reverse flow in line 112 r from chamber 114 back to valve 60a.

Volume chamber 114 is connected to one outlet of tee 88 by line 113. The remaining outlet of tee 88 is provided with bleed line 118, having manual valve 120 for opening or closing bleed line 118. Pressure gauges 121, 122, 123 and 124 provide a visual indication of the pressure. in the sales line, holding chamber, tubing line,.and on the low pressure side of orifice 35.

FIG. 3 shows schematically the hydraulic system of FIG. 2. The system shown in FIGS. 2 and 3 will be better understood from the following description of operation of the control system. Controller 25 is connected to a conventional gas well 10 as shown in FIG. 1 with motor control valve 22 located in the discharge line 20 of the well communicating the discharge line with sales line 24. Gas from the formation flows from the well through tubing string 16 and discharge line 20 to sales or flow line 24 to be delivered to a suitable destination. As is well known, the pressure in sales line 24 is maintained by pumps or compressors along the delivery route.

Valve 22 is provided with controller 30 of the diaphragm type. The diaphragm controller as is conventional, operates to open control valve 22 when the pressure signal is delivered to the controller to overcome the spring bias urging the control valve 22 to a closed position. A flow sensing element is placed in either the discharge line 20 or the sales line 24 adjacent valve 22 to measure the production of the well. The flow sensing element 35 may be a flow nozzle, venturi or an orifice. Pressure taps are connected across the orifice and the differential pressure is transmitted to the automatic gas well controller 25 by lines 36, 38 and 40. The pressure in line 36 represents the pressure within the tubing string and the pressure upstream of flow sensing device 35. Pressure in line 36 is communicated to lower diaphragm chambers 52 and 52a of pilot valve assemblies 42 and 44 respectively. The downstream or low side differential pressure across flow sensing device 35 is communicated by line 38 to diaphragm chamber 48a of pilot valve assembly 44. The pressure existing in the sales line 24 is communicated by line 40 to diaphragm chamber 48 of pilot valve 42. Pilot valve 42 is responsive to the differential pressure existing between the sales line and the tubing line. Pilot valve assembly 44 is responsive to the rate or gas flow velocity measured by the differential pressure existing across flow control device 35.

A gas supply from an existing line 73 or suitable compressor or other source supplies filter 74. The filter is connected to a conventional regulator which provides a regulated gas supply pneumatic valves 60, 60a and 86 via lines 81, 82 and 87 respectively. The output signal from valve 60 is communicated to cylinder chamber 103 of cylinder 98 by line 106 to cause actuation of valve 86 upon pressurization of cylinder chamber 103. Similarly, the signal from valve 60a is communicated to pressure chamber 105 of cylinder by line 108. The signal from valve 60a communicates with volume chamber 114 by line 112 across check valve 116. One outlet of tee fitting 88 connects line 32 to the pressure chamber of controller 30. Fitting 88 is also connected with the outlet 91 of valve 86 across check valve 117 and communicates with the interior of accumulator or volume chamber 114. The remaining outlet of tee fitting 88 is provided with a bleed line 118 controlled by a manual valve 120.

When it is desired to open the well only when the differential pressure between the tubing and the sales line is above a selected differential, e.g., a differential pressure of 200 p.s.i., the operation of the system is as follows: At differential pressures below this level, the pressure in tubing line 16 is too low to produce a sufficient gas volume from the well and liquid accumulations will occur in the well and flow from the well will continue to decrease substantially. Spring 56 in pilot valve assembly 42 is accordingly selected to determine the pressure differential at which valve 60 is actuated.

Orifice 35 is properly calibrated and spring 56a selected so that plunger 58a is moved upward into engagement with actuator 62a of valve 60a when the differential pressure across the orifice 35 drops below a predetermined level. For example, orifice 35 and spring 56a are selected so that a differential pressure of less than 5 psi. is indicative of a flow rate of less than 300,000 cubic feet per day, and accordingly, will cause the reduced pressure in chamber 52a to be overcome by the action of biassing spring 56a and the pressure in chamber 48a to disengage plunger 58a from actuator 62a causing valve 60a to open terminating the signal to controller 30, closing control valve 22.

During normal operation of the well and with sufficient production from the well, the proper differential pressure will be maintained between the tubing and sales lines. The sufficiently higher tubing pressure will cause the pressure in diaphragm chamber 52 to overcome the combined biassing force of the pressure in diaphgram chamber 48 and the force of spring 56 urging plunger 58 upwardly into contact with pin 62 of valve 60. Depression of pin 62 will cause a pressure signal to be sent to pressure chamber 103 of cylinder 98. Pressure in cylinder chamber 103 will exert a force against piston 99 moving the piston into contact with pin 94 of valve 86. Depression of pin 94 will open valve 86 to permit a pressure signal to be discharged at outlet 91 and across check valve 117 to fitting 88. The pressure supply is sent via line 32 to the chamber of valve controller 30 causing valve 22 to open and permit flow of gas from the well.

Immediately as flow is established. a pressure differential will be established across flow control element 35. This differential pressure is transmitted to opposite sides of diaphragm 50a in pilot valve assembly 44. At sufficient flow rates, the pressure differential across the flow control device 35 will exceed the setting of spring 56a. Thus, plunger 58a will be urged into contact with pin 62a, depressing pin 62a to send a pressure signal from valve 60a across tee 110 and through line 108 to chamber 105 of cylinder 100. Pressurization of cylinder chamber 105 will move piston into engagement with pin 96. Depression of pin 96 will move the valve spool of valve 86 leftwardly, terminating flow across valve 86.

The pressure signal from pilot valve 44 will also be simultaneously delivered across check valve 116 and through line 112 to the interior of chamber 114 and to the controller 30 of valve 22. Thus, immediately upon discontinuance of the transmission of a pressure signal across valve 86, a by-pass signal is established directly to the valve controller through line 112. As long as the flow rate and velocity of production from the well is sufficient, valve 60a in pilot 44 will be held in an open position under the influence of plunger 58a. A decrease in the velocity or rate of flow from the well will permit fluid to fall back and load the tubing and be reflected by a reduction in the differential pressure across flow control element 35. When the differential drops below the setting of spring 56a, plunger 58a will disengage pin 62a terminating supply of pressure to the valve controller. Valve 22 is normally biased to a closed position. Pressure in valve controller 30 is permitted to bleed slowly from the valve controller and volume chamber 114 through line 118 and valve 120. The metered bleed-off of pressure from the valve controller 30 dampens actuation of control system so that the control valve will not tend to oscillate or cycle in response to rapid changes in flow rate. Check valves 116 and 117 prevent pressure in the accumulation chambers 114 from bleeding back across either valve 600 or valve 86.

Once the well is shut-in, pressure within the tubing will begin to build and when the tubing and sales line differential pressure is sufficient to deliver gas at an acceptable volumetric rate, the pressure in diaphgram chamber 52 will again urge plunger 58 upwardly, opening valve 60 to cause a pressure signal to be delivered to the controller of valve 22. The control cycle will again be repeated in the manner described above with pilot 44 discontinuing the pressure signal to control valve 22 when the gas flow rate again decreases to a point that fluid within the well begins reloading the tubmg.

In summary, the present invention contemplates a method and an apparatus for automatically controlling production from a gas well by shutting-in the well under predetermined conditions and maintaining the shut-in condition until the pressure differential builds to an acceptabel level. .As described above, the well is allowed to produce when the differential between the tubing and sales line is sufficient to produce at an economical volumetric rate. The well remains open until the flow rate decreases to a point that the tubing begins to load with fluid.

The present invention has been described specifically with reference to a gas well, however, it is to be understood that the present invention has application to other types of petroleum wells such as oil wells. particularly those having gas-oil ratios above 2,000 to I. Also, it will be appreciated that the control valve could be provided with an electrical operator and electric micro-switches in place of valves 60, a and 86 to achieve the same control functions. Such an alternative embodiment of pneumatic valve 60 is illustrated in FIG. 4, the equivalent parts in FIGS. 3 and 4 having been designated with identical reference numerals. The circuit of FIG. 4 differs from the corresponding portion of the circuit of FIG. 3 in that the circuit of FIG. 4 comprises solenoid operated valve 60' as an alternative to pneumatic valve 60. Such solenoid operated valve is actuated in response to signals received from pressure responsive micro-switches and 132 which are in turn connected to the chambers 48 and 52 as in FIG. 3. In a similar manner, electrically operated valves may be substituted for pneumatic valves 60a and 86.

As illustrated in FIG. 5, valve 22 may be alternatively operated by a controller 30 which comprises solenoid 30a driven by actuator 30b. Actuator 30b responds to pressure conducted through line 32 and in turn actuates solenoid 30a to close valve 22.

From the foregoing, it can be seen that the present invention provides a simple, effective control for gas wells. The control system of the present invention is particularly adaptable to low-production wells. Using the control system of the present invention, lowproducing wells that formerly were plugged because production from these wells was economically unfeasible, now can be operated profitably. Using the control system of the present invention which monitors sales and tubing pressure and flow rate from the well. the well is controlled so that it is shut-in before excessive fluid accumulation occurs in the well tubing. In this way, it is not necessary to intermit the well to expel excessive fluid to the atmosphere.

With the installation of the present invention, all control equipment is conveniently accessible at the surface of the well. The control system of the present invention can be adjusted in accordance with a particular well and the desired control parameters. Once the control is set at an optimum flow rate, it will continue to operate under the same conditions automatically without manual intervention.

The present invention is subject to numerous modifications and changes as will readily occur to those skilled in the art. It is not desired to limit the invention to the construction and operation shown and described, and accordingly, all such modifications and changes are intended to be within the spirit and scope of the present invention as claimed.

what is claimed is: l. A control apparatus for a petroleum well having a tubing string and discharge line discharging into a sales line comprising:

a control valve interposed between said tubing string and sales line adapted to open or shut-in said well;

flow sensing means for monitoring the petroleum flow from said well and adapted to close said valve to shut-in said well when the flow decreases below a predetermined rate; and

pressure monitoring means for measuring the pressure differential between the tubing string and sales line and adapted to open said valve permitting delivery of petroleum from said well only when a predetermined differential therebetween exists whereby said well remains shut-inuntil the differential pressure builds to a level for acceptable volumetric flow from the well.

2. The apparatus of claim 1 whereby said flow sensing means comprise restriction means in said discharge line and a differentialpressure flow sensing device operatively connected across said flow sensing means.

3. The apparatus of claim 1 wherein said pressure monitoring means comprises a differential pressure pilot valve.

4. The apparatus of claim 1 wherein said control valve has-a solenoid operator and said flow sensing means and said pressure monitoring means include electrical switch means adapted to send an operative signal to said solenoid operator.

5. A control apparatus for a flowing gas well having a tubing string and discharge line connected to a sales line, said apparatus'comprising:

a control valve located intermediate said discharge line and said sales line having a controller adapted to operate said valve to open or shut-in said tubing string;

a first differential pilot valve monitoring the pressure differential between the tubing and sales lines and including first valve means adapted to operate said control valve to open said well only when the tubing pressure exceeds the sales line pressure by a predetermined differential;

a second differential pilot valve including second valve means adapted to operate said control valve to shut-in the well when the flow rate decreases below a predetermined rate whereby said first pilot valve opens'said control valve only when said tubing string pressure is adequate for delivery of an acceptable gas volume flow and said second pilot valve closes said control valve thereby shutting-in said well when said flow rate decreases below said predetermined rate.

6. A control apparatus for a flowing gas well having a tubing string and discharge line connected to a sales line comprising:

a motor control valve located intermediate said discharge line and said sales lines, said motor control valve biassed to a closed position normally shutting-in said well;

valve controller means operating said motor control valve adapted to open said valve when a pressure signal is supplied thereto;

a first differential pilot valve having a chamber divided into first and second pressure chambers by a diaphragm, said first pressure chamber adapted for connection to monitor said tubing string pressure and said second pressure chamber adapted for connection to monitor said sales line pressure, plunger means operatively connected to said diaphragm, normally closed first pneumatic valve means operably connected to said plunger means whereby said pneumatic valve means emits a signal when the tubing pressure exceeds thesales line pressure by a predetermined differential;

a second differential pilot valve having a chamber divided into third and fourth pressure chambers by a diaphragm, a flow sensing restriction connected between said third and fourth pressure chambers whereby the differential pressure across said flow sensing restriction is monitored by said second 5 pilot valve, plunger means operatively connected to said diaphragm, normally open second pneumatic valve means operably connected to said plunger means whereby the pressure signal from said pneumatic valve means is terminated when the pressure differential across said flow sensing restriction decreases to a predetermined level;

pneumatic switching valve means having a first open position adapted to direct a signal pressure to said motor control valve to open said valve and a second closed position, said pneumatic valve means connected to said first and second pilot valves whereby actuation of said first pilot valve activates said switching valve means to open and actuation of said second pilot valve causes said switching valve means to close;

by-pass means for supplying a signal from said second pilot valve to said valve controller means by passing said switching valve means; and

vent means for venting said valve controller means whereby said motor control valve will be opened by a signal from said first pilot valve when the tubing string and sales line differential reaches a predetermined level and will be held open by a signal from said second pilot valve through said by-pass means until said flow rate drops below a predetermined level and upon cessation of a pressure signal to said valve controller means pressure will be relieved via said vent means to permit said control valve to close.

7. The apparatus of claim 6 including a pressure regulator for supplying a regulated supply of gas to said first and second pneumatic valve means and said pneumatic switching valve means.

8. The apparatus of claim 6 wherein said pilot valves are adjustable relative to said plunger means to adjust the responsiveness of the control.

9. The apparatus of claim 6 wherein said switching valve means is operable by means of a reciprocable spool and includes first and second actuator means associated with opposite spool ends for reciprocating said spool between said open and closed position.

10. The apparatus of claim 9 wherein said first differential pilot valve is connected to said first actuator means and said second differential pilot valve is connected to said second actuator means whereby said first pilot valve opens said switching valve means and said second pilot valve closes said switching valves means as a pressure is established to said controller means via said by-pass means.

11. The apparatus of claim 6 including an accumulator chamber intermediate said pneumatic switching valve means and said controller means.

12. The apparatus of claim 11 wherein one-way check valves are interposed at the inlet and outlet of said accumulator to prevent pressure in said accumulator from venting at said switching valve means and pilot valves.

13. A petroleum well system comprising:

a tubing line extending into a petroleum formation having an open lower end for admitting flow;

a sales line;

a control valve interposed between said tubing line and adapted to open said valve permitting delivery of petroleum from said well only when a predetermined differential exists therebetween whereby said well remains shut-in until the pressure differential builds to a level for acceptable volumetric flow from the well. 

1. A control apparatus for a petroleum well having a tubing string and discharge line discharging into a sales line comprising: a control valve interposed between said tubing string and sales line adapted to open or shut-in said well; flow sensing means for monitoring the petroleum flow from said well and adapted to close said valve to shut-in said well when the flow decreases below a predetermined rate; and pressure monitoring means for measuring the pressure differential between the tubing string and sales line and adapted to open said valve permitting delivery of petroleum from said well only when a predetermined differential therebetween exists whereby said well remains shut-in until the differential pressure builds to a level for acceptable volumetric flow from the well.
 2. The apparatus of claim 1 whereby said flow sensing means comprise restriction means in said discharge line and a differential pressure flow sensing device operatively connected across said flow sensing means.
 3. The apparatus of claim 1 wherein said pressure monitoring means comprises a differential pressure pilot valve.
 4. The apparatus of claim 1 wherein said control valve has a solenoid operator and said flow sensing means and said pressure monitoring means include electrical switch means adapted to send an operative signal to said solenoid operator.
 5. A control apparatus for a flowing gas well having a tubing string and discharge line connected to a sales line, said apparatus comprising: a control valve located intermediate said discharge line and said sales line having a controller adapted to operate said valve to open or shut-in said tubing string; a first differential pilot valve monitoring the pressure differential between the tubing and sales lines and including first valve means adapted to operate said control valve to open said well only when the tubing pressure exceeds the sales line pressure by a predetermined differential; a second differential pilot valve including second valve means adapted to operate said control valve to shut-in the well when the flow rate decreases below a predetermined rate whereby said first pilot valve opens said control valve only when said tubing string pressure is adequate for delivery of an acceptable gas volume flow and said second pilot valve closes said control valve thereby shutting-in said well when said flow rate decreases below said predetermined rate.
 6. A control apparatus for a flowing gas well having a tubing string and discharge line connected to a saLes line comprising: a motor control valve located intermediate said discharge line and said sales lines, said motor control valve biassed to a closed position normally shutting-in said well; valve controller means operating said motor control valve adapted to open said valve when a pressure signal is supplied thereto; a first differential pilot valve having a chamber divided into first and second pressure chambers by a diaphragm, said first pressure chamber adapted for connection to monitor said tubing string pressure and said second pressure chamber adapted for connection to monitor said sales line pressure, plunger means operatively connected to said diaphragm, normally closed first pneumatic valve means operably connected to said plunger means whereby said pneumatic valve means emits a signal when the tubing pressure exceeds the sales line pressure by a predetermined differential; a second differential pilot valve having a chamber divided into third and fourth pressure chambers by a diaphragm, a flow sensing restriction connected between said third and fourth pressure chambers whereby the differential pressure across said flow sensing restriction is monitored by said second pilot valve, plunger means operatively connected to said diaphragm, normally open second pneumatic valve means operably connected to said plunger means whereby the pressure signal from said pneumatic valve means is terminated when the pressure differential across said flow sensing restriction decreases to a predetermined level; pneumatic switching valve means having a first open position adapted to direct a signal pressure to said motor control valve to open said valve and a second closed position, said pneumatic valve means connected to said first and second pilot valves whereby actuation of said first pilot valve activates said switching valve means to open and actuation of said second pilot valve causes said switching valve means to close; by-pass means for supplying a signal from said second pilot valve to said valve controller means by-passing said switching valve means; and vent means for venting said valve controller means whereby said motor control valve will be opened by a signal from said first pilot valve when the tubing string and sales line differential reaches a predetermined level and will be held open by a signal from said second pilot valve through said by-pass means until said flow rate drops below a predetermined level and upon cessation of a pressure signal to said valve controller means pressure will be relieved via said vent means to permit said control valve to close.
 7. The apparatus of claim 6 including a pressure regulator for supplying a regulated supply of gas to said first and second pneumatic valve means and said pneumatic switching valve means.
 8. The apparatus of claim 6 wherein said pilot valves are adjustable relative to said plunger means to adjust the responsiveness of the control.
 9. The apparatus of claim 6 wherein said switching valve means is operable by means of a reciprocable spool and includes first and second actuator means associated with opposite spool ends for reciprocating said spool between said open and closed position.
 10. The apparatus of claim 9 wherein said first differential pilot valve is connected to said first actuator means and said second differential pilot valve is connected to said second actuator means whereby said first pilot valve opens said switching valve means and said second pilot valve closes said switching valves means as a pressure is established to said controller means via said by-pass means.
 11. The apparatus of claim 6 including an accumulator chamber intermediate said pneumatic switching valve means and said controller means.
 12. The apparatus of claim 11 wherein one-way check valves are interposed at the inlet and outlet of said accumulator to prevent pressure in said accumulator from venting at said switching valve means and pilot valves.
 13. A petRoleum well system comprising: a tubing line extending into a petroleum formation having an open lower end for admitting flow; a sales line; a control valve interposed between said tubing line and sales line adapted to open or shut-in said well; flow sensing means for monitoring the petroleum flow from said well and adapted to close said valve to shut-in said well when the flow decreases below a predetermined rate; and pressure monitoring means for measuring the pressure differential between the tubing and sales line and adapted to open said valve permitting delivery of petroleum from said well only when a predetermined differential exists therebetween whereby said well remains shut-in until the pressure differential builds to a level for acceptable volumetric flow from the well. 